Requirements of calcium fluxes and ERK kinase activation for glucose- and interleukin-1β-induced β-cell apoptosis

Increasing evidence indicates that beta-cell apoptosis and impaired secretory function were partly mediated by interleukin (IL)-1 beta and/or high-glucose-induced beta-cell production of IL-1 beta. However, the specific signal transduction pathways and molecular events involved in beta-cell dysfunction remain largely unresolved. In this study, we investigated whether Ca(2+) and extracellular signal-regulated kinase (ERK) activation plays a role for IL-1 beta action in rat islets. Exposure of rat islets for 4 days to 33.3 mM glucose and 140 ng/ml IL-1 beta- induced beta-cell apoptosis and impaired glucose-stimulated insulin secretion. By Western blotting with phosphospecific antibodies, glucose and IL-1 beta were shown to activate ERK. Ca(2+) channel blocker nimodipine or ERK inhibitor PD98059 prevented glucose- and IL-1 beta-induced ERK activation, beta-cell apoptosis, and impaired function. Furthermore, treatment with Ca(2+) ionophore ionomycin, or exposure to thapsigargin, an inhibitor of sarco(endo)plasmic reticulum Ca(2+) ATPase, all caused an amplification of IL-1 beta-induced ERK activation in rat islet. On the other hand, a chelator of intracellular free Ca(2+) [bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid-acetoxymethyl] (BAPTA/AM) and an inhibitor of calmodulin (W7) diminished IL-1 beta-induced phosphorylation of ERK. Finally, islet release of IL-1 beta in response to high glucose could be abrogated by nimodipine, mibefradil, or PD98059. Together, these data suggest that glucose- and IL-1 beta-induced beta-cell secretory dysfunction and apoptosis are Ca(2+) influx and ERK dependent in rat islets.